The role of chronic muscle overuse in patients with a neuronal deficit leading to partially denervated muscles in unclear, poliomyelitis is just one of the many neurogenic disorders which produce a neuronal deficit and partially denervated muscles. It now appears that patients who have had polio, 20 to 30 years ago, are now experiencing sequela, such as muscle weakness, muscle pain, etc., which appear to be related to their original illness. These late effects of polio, termed the Post-Polio Syndrome, can produce loss of function, productivity, and reversal of rehabilitation gains. One hypothesis to explain this syndrome is that its sequela is caused by chronic muscle overuse. Which level(s) of the motor unit are affected is not known at present. We propose that chronic overuse will (1) precipitate a loss of motoneurons which are hyperfunctioning and overexpanded, (2) impair sprouting, (3) produce alterations at the neuromuscular junction, and (4) induce alterations in the muscle fibers. It is our belief that these effects will be more pronounced over time. Therefore, the broad, long-term objectives of our proposed study is to electrophysiologically, histochemically, and morphologically examine the number of motoneurons, degree of sprouting, neuromuscular junction, muscle fibers and fiber type pattern in a model of neuromuscular dysfunction having a neuronal deficit and partially denervated muscles. We intend to partially denervate and examine the plantaris muscle of rat every month for a total of 10 months. Changes seen in the overused, partially denervated muscles will be compared to muscles from sham operated rats and to muscles from nonoperated rats. It is anticipated that results from this study will enable clinicians to better assess the long-term effects of chronic muscle overuse in patients having partially denervated muscles. The patient population to be targeted by our study are the over 300,000 persons who have developed polio during the epidemics of the 1930's to mid-1950' as well as individuals with other neurogenic disorders which produce partially denervated musculature.